Abstract
This study examined the difference in the dynamic visual acuity test (DVAT) between collegiate athletes who are deaf or hard-of-hearing (D/HoH) (n = 38) and university club-level athletes who are hearing (n = 38). Dynamic visual acuity was assessed using the Bertec Vision Advantage (Bertec® Corporation, Columbus, Ohio, USA). No statistically significant differences between athletes who are D/HoH and who are hearing were found in DVAT for leftward (χ2 = 0.71, p = 0.40) or rightward (χ2 = 0.04, p = 0.84) head yaw rotation around an earth vertical axis. Dynamic visual acuity was similar for athletes regardless of hearing status. Baseline DVAT data may be of use for post-injury management of athletes who are D/HoH.
Introduction
An estimated 1.6 to 3.8 million sports-related concussions occur in the United States annuallyCitation1 accounting for 5.8% of all injuries in collegiate athleticsCitation2 with the majority occurring in football and female soccer.Citation3 These staggering numbers warrant health care providers to be appropriately equipped to educate and manage concussions across diverse cohorts of athletes.Citation3
An estimated 190,000 post-secondary students are deaf or hard-of-hearing (D/HoH) in the United States.Citation4 Individuals who are deaf have profound hearing loss while individuals who are hard-of-hearing have slight to severe hearing loss.Citation5 Many students participate in athletics ranging from collegiate club to National Collegiate Athletic Association (NCAA) sports; Citation6 regardless of competition level, athletic participation puts athletes who are D/HoH at risk for concussion.Citation7 Although little is known on concussion management for athletes who are D/HoH, reports indicate that they have a similar concussion rate to athletes who are hearing.Citation8 According to the International Conference on Concussion in Sport, it is recommended that concussions in special populations, including athletes who are D/HoH, should be managed differently.Citation9
Due to the proximity of the vestibular apparatus to the cochlea, individuals who are D/HoH may exhibit vestibular dysfunction.Citation10 Decreased cognitive performanceCitation11 and prolonged recoveryCitation12,Citation13 are associated with vestibular dysfunction following sport-related concussion. Of those who sustain a sports-related concussion, approximately 50% experience vestibular dysfunctionCitation14 leading to a 6.4 times greater risk of protracted recoveryCitation15 including increased likelihood of post-concussion syndromeCitation12 and delay in return to academic study.Citation13
A crucial function of the vestibular system is vestibular-ocular reflex (VOR) which coordinates eye movements for clear vision during head movements.Citation16 Performance-based VOR assessments, such as the dynamic visual acuity test (DVAT), serve as objective measures to quantify VOR and VOR function via visual-vestibular interactions.Citation17 Implementing DVAT may identify clinical deficits not detected by other concussion assessments, especially in special populations. Previous authors suggest that decreased phases and VOR symmetry are poorer in some individuals who are D/HoH suggesting vestibular dysfunction.Citation18,Citation19 However, others have found that factors, such as sport participation and the use of the visuospatial language, American Sign Language (ASL), may positively influence dynamic visual acuity (DVA) performance.Citation20,Citation21
To our knowledge, no evidence currently exists regarding VOR function of young adult athletes who are D/HoH; due to potential vestibular dysfunction, VOR of athletes who are D/HoH may not be accurate. If discrepancies are not identified, it may negatively influence management and return-to-play decisions for these athletes. This study aimed to investigate (1) differences in DVAT between athletes who are D/HoH and athletes who are hearing and (2) differences in DVAT between athletes who are deaf and those who are hard-of-hearing. We hypothesized that athletes who are D/HoH would have poorer DVAT performance compared to athletes who are hearing, and athletes who are deaf would have poorer DVAT performance compared to athletes who are hard-of-hearing.
Methods
Participants
Collegiate varsity athletes who are D/HoH from an NCAA Division III institution and club level athletes who are hearing from a different institution. Collegiate club athletes compete against other institutions but do not have varsity status. Eligible participants were athletes aged 18 to 30 years, and self-reported as either D/HoH or hearing; deaf was identified as profound hearing loss (91+ decibel loss), hard-of-hearing was slight to severe hearing loss (16–91+ decibel loss), and hearing was −10 to 15 decibel loss.Citation5 Exclusion criteria included a medical diagnosis of: (1) concussion within 6 months of data collection, (2) current post-concussion syndrome, (3) a mental health condition or legal blindness, and (4) current pregnancy.
All participants were contacted and recruited via email. Athletes who were D/HoH could view the consent form via ASL interpreted video. All participants were required to sign a paper consent form. A study member who could communicate in ASL and English was present during the consent process and data collections.
Instrumentation
The Bertec Vision Advantage (Bertec® Corporation, Columbus, Ohio, USA) was used to perform the DVAT via inertial measurement unit (sampling frequency 175 Hz). The device was placed on the participant’s forehead, held by a headband, to measure velocity and directionality of head rotations. All DVAT outcomes were in Logarithm of Minimum Angle of Resolution (LogMar) units.
Questionnaire
Participants answered questions regarding sex, primary sport participation, history of concussion(s) and hearing status prior to data collection. Additionally, athletes who are D/HoH answered questions regarding hearing loss onset, history of cochlear implantation surgery, and self-reported degree of hearing loss on each side.
Assessments
Baseline visual acuity (BLVA), visual processing time (VPT), and DVAT were assessed using the Bertec Vision Advantage. BLVA and VPT were used as DVAT baseline measurements. Participants were permitted to wear corrective contact lenses during all testing if they used them during sport participation. Glasses were prohibited due to a prismatic effect that could influence the results. Participants sat five feet away from the computer screen at eye level.
To assess BLVA, a blocked-letter letter “E” (optotype) flashed on the screen pointed in one of four directions (up, down, left, or right). Participants were asked to identify the direction of the optotype when it disappeared from the screen. For BLVA, the optotype grew larger for a wrong answer and smaller for a correct answer until the software algorithm calculated BLVA. The same methodology was used to assess VPT except the optotype remained on the screen longer for incorrect answers and for less time with correct answers. The shortest VPT allowed was 30 milliseconds.
To assess DVA, the participant’s head was passively rotated 20° in each direction with a target velocity of 100°/sec in rotation around an earth vertical axis per the Bertec Vision Advantage DVA protocol. DVA was assessed with a maximum of 20 trials for each side until the software algorithm determined DVA.
Statistical analysis
Descriptive statistics were run to report demographics. Chi-square exact tests were performed to assess the association between demographics and hearing status. Preliminary Wilcoxon Rank Sum tests revealed that sex (leftward DVA: p = 0.23; rightward DVA: p = 0.65) and concussion history (leftward DVA: p = 0.30; rightward DVA: p = 0.70) were not significant factors; therefore, they were not included in the final model.
Kruskal-Wallis tests were run to identify if differences existed in leftward and rightward DVA between (1) athletes who are hearing and D/HoH and (2) athletes who are deaf and who are hard-of-hearing. DVA was determined by subtracting the BLVA LogMAR score from the DVA LogMAR score. RStudio v4.0.2 (The R Foundation for Statistical Computing) was used for all analyses. Alpha was set a priori at 0.05.
Results
Thirty-eight athletes who are D/HoH (age: 20.89 ± 2.20 yrs., height: 1.74 ± 0.12 m., weight: 74.77 ± 17.04 kg.) and 38 athletes who are hearing (age: 20.68 ± 1.32 yrs., height: 1.76 ± 0.09 m., weight: 77.40 ± 12.75 kg.) volunteered. presents demographics for the entire sample.
Table 1. Participant demographics.
BLVA was −0.21 ± 0.63 LogMar for athletes who are hearing and −0.12 ± 0.14 for athletes who are D/HoH. There were no associations between hearing status and DVA yaw rotation to the right (hearing: −0.11 ± 0.87 LogMAR; D/HoH: −0.13 ± 0.11 LogMar) (χ2 =0.04, p = 0.84) or left (hearing: −0.09 ± 0.18 LogMAR; D/HoH: −0.10 ± 0.99 LogMAR) (χ2=0.71, p = 0.40). Twenty-two of the 38 athletes who are D/HoH as well as 32 of the 38 athletes who are hearing had different responses for right and left DVA.
Of those athletes who are D/HoH, 12 males who are hard-of-hearing and 19 males and 7 females who are deaf participated. Hearing loss status was significantly associated with sex (χ2 (1, n = 38) = 3.96, p = 0.04), time of hearing loss (χ2 (1, n = 38) = 7.44, p = 0.02), history of cochlear implant surgery (χ2 (1, n = 38) = 6.26, p = 0.01), right side degree of hearing loss (χ2 (1, n = 38) = 11.58, p = 0.02), and left side degree of hearing loss (χ2 (1, n = 38) = 15.60, p < 0.01). There were no associations between hearing loss status and DVA yaw rotation to the right (χ2 =0.67, p = 0.41) or left (χ2 =0.38, p = 0.51) ().
Discussion
Understanding DVA performance of athletes who are D/HoH may assist in rehabilitation programs, concussion management, and return-to-play decisions following injury. This study compared DVA performance of athletes who are D/HoH with athletes who are hearing; findings revealed no significant differences between the groups, though individual differences were noted. Analyses also revealed no differences in DVA performance between athletes who are deaf and athletes who are hard-of-hearing; however, caution should be taken with these results due to small sample size.
Although a considerable amount of research has investigated vision in individuals who are D/HoH, there is limited information available on DVA performance of adults who are D/HoH. It is suggested that individuals who are D/HoH have larger peripheral visual fieldCitation22 and better peripheral field visual performanceCitation23 but similar central visual performanceCitation24,Citation25 when compared to individuals who are hearing. Findings from Nakajima et alCitation26 suggest that DVA performance from individuals who are hearing were poorer on average compared to Deaflympic athletes who are D/HoH.Citation26 It should be noted that athletes who are hearing “engaged in sports” without additional clarification on the extent of their sport participation.Citation26 Nakajima et alCitation26 used a different device and assessment to quantify DVA than what was used in this study. Due to methodology differences, caution should be taken when comparing findings from the current study to those from Nakajima et al.Citation26
Participation in sport may aid in the development and sustainability of DVA performance of athletes who are D/HoH. Previous authors have suggested that individuals who participate in sport have superior DVA performance compared to individuals who do not;Citation20 it may be appropriate to assume then that individuals who are D/HoH and participate in sport may have improved DVA performance. Many individuals who are D/HoH use ASLCitation21, a visuospatial language, as their primary mode of communication,Citation6,Citation27 which may influence DVA performance. The combination of sport participation and frequently engaging in ASL, visuospatial language may enhance DVA of athletes who are D/HoH to a level better than non-athletes and non-signers who are D/HoH or comparable to athletes who are hearing.
Our results suggest there are no significant differences in DVA performance between athletes who are deaf and athletes who are hard-of-hearing. To the authors’ knowledge, no literature exists which investigates the influence of degree of hearing loss on DVA performance. However, our results do not support findings of previous postural control literature which suggests that the greater the degree of hearing loss, the greater the degree of vestibular dysfunctionCitation28 among individuals who are D/HoH.Citation29 Self-reported degree of hearing loss may not have been accurate and thus may have influenced DVA performance of athletes who are D/HoH.
Healthcare professionals should consider DVA performance of athletes who are D/HoH and athletes who are hearing on an individual basis. Collecting additional baseline data of athletes who are D/HoH, such as postural controlCitation30 and neurocognitive assessments,Citation31 will help confirm associations. Healthcare professionals may compare post-injury DVA scores of athletes who are D/HoH with existing normative data to see if differences exist; origin of normative data and level of competition should be considered to ensure appropriate comparisons.
There are limitations to note from this study. Competition level was different between hearing groups. Additionally, hearing status was self-reported and therefore, may have been inaccurate. Although participants were allowed to wear contact lenses during testing, this may have influenced findings. Additionally, participant visual information such as refractive errors was not collected and may have influenced the results. Lastly, previous authors have suggested sport activity may influence DVA performance;Citation20,Citation32 due to the small sample size and a large distribution of sport participation, sport was not included as a factor in the analysis. Future research should take objective hearing loss measures to look at the impact of degree of hearing loss on DVA as well as investigate the impact of sport participation, use of ASL, and history of cochlear implantation surgery on DVA.
Conclusion
Hearing status did not influence DVA performance. Baseline assessment data is highly desirable; however, these findings suggest that baseline DVA scores may not be necessary for athletes who are D/HoH. Healthcare providers may be able to use existing normative DVA data to assist in concussion management and return-to-play decisions.
Conflict of interest disclosure
The authors have no conflicts of interest to report. The authors confirm that the research presented in this article met the ethical guidelines, including adherence to the legal requirements of the United States and received approval from the Institutional Review Board of The Ohio State University.
Additional information
Funding
References
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